1 Practical Interpretation of Unbroken Chain in Metrological Traceability as to VIM 3 Center for Measurement Standards (CMS) Industrial Technology Research Institute (ITRI) Authors: Yi-Ting Chen, Lung-Hen Chow, Liang-Hsing Chen, and Gwo-Sheng Peng

2 Outline 1.Introduction 2.Definition of “Metrological traceability” in VIM 3 3.Typical Metrological Traceability Diagram 4.Additional Mathematical Description 5.Case study - Gauge Block Measurement 6.Discussion and Conclusion

3 Introduction

4 Clear the addresses of VIM –ISO/IEC Guide 99:2007, “International vocabulary of metrology — Basic and general concepts and associated terms” cancels and replaces the old VIM:1999. The term “Traceability” is replaced by “Metrological traceability” –a new definition as property of a measurement result which can be related to a reference –an evidence of measurands tracing to the primary standards which can realize the SI units –a documented unbroken chain of calibrations

5 Introduction National Measurement Laboratory (NML, the NMI in Taiwan) has operated its mission since Effective knowledge transfer has become an essential issue. Gauge block measurement is demonstrated for such purpose at NML. In dealing with definition of “metrological traceability” in VIM 3, additional mathematical description is taken to enhance the practical interpretation of the definition.

6 Definition of “Metrological traceability” in VIM 3

7 Definition of metrological traceability in VIM 3 Definition of this term in VIM 3 : 2.41 metrological traceability Property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty. 2007

8 Metrological traceability Property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty. Unbroken chain of calibrations Metrological traceability Measurement result Calibration Measurement Result Measurand Reference Measurement standard Measurement procedure Measurement unit Measurement uncertainty Measured quantity value & document

9 Six important elements in ILAC P an unbroken chain 2. uncertainty of measurement 3. documentation 4. competence 5. reference to SI units 6. calibration intervals The International Laboratory Accreditation Cooperation (ILAC) also proposed six important elements to confirm the definition of “metrological traceability” : 2.41 Metrological Traceability : Property of a measurement result whereby the result can be related to a reference 5 through a documented 3 unbroken chain 1 of calibrations 6, each contributing to the measurement uncertainty 2.

10 Typical metrological traceability diagram

11 Typical metrological traceability diagram Hardness traceability chain in Metrologia 47(2010) S59–S66 (Traceability in hardness measurements: from the definition to industry)

12 For a specific measured quantity of calibration at NML, there will be two documents: –Instrument Calibration Technique (ICT) –Measurement System Validation Procedure (MSVP). Typical approach of NML’s metrological Traceability Diagram Gauge block comparator measurement traceability diagram Mass measurement system traceability diagram Measurement System Validation Procedure (MSVP). The traceability illustration in figures cannot fully cover the aforementioned six important elements of metrological traceability.

13 Additional Mathematical Description

14 Additional Mathematical Description Combine “mathematical measurement equation” with typical metrological traceability diagram to reinforce the evidence of “unbroken chain of calibrations”. In order to really focus on the property of measurement result as metrological traceability defined in VIM 3, we shall emphasize the output quantity in the measurement model or equation.

15 Case study - Gauge Block Measurement

16 Gauge Block Comparator calibration system Metrological traceability of gauge block measurement SI unit length (m) Gauge Block Interferometer calibration system Frequency Stabilized Lasers calibration system Fequency stabilized laser, f  λ, wavelength ： nm Standard gauge block, L r 0.5 mm to 100 mm Gauge block measurement result Gauge block measurement result Measured difference, d 1 (  m ) Gauge block, L X 0.5 mm to 100 mm Deviation, d 2 (  m )  The left-hand parameter of the equation is unknown and the right-hand parameters are known.  In mathematical approach, an unbroken chain is demonstrated and measurement result of each step traced to the measurand of the previous step. MeP Fequency Stabilized laser, f r, (Iodine stabilized He-Ne laser ) SI unit : length (m) Frequency deviation, △ f (kHz) 1. an unbroken chain 5. reference to SI units

17 SI units platinum resistance thermometer dew point hygrometer U = 0.20 ℃ B B C Metrological traceability of auxiliary parameters NML the fixed-point calibration system for platinum resistance thermometers (T05) NML two- pressure humidity generator calibration system (H01) K K Pa standard resistor digital pressure gage U = 20 µ   U = kPa C970374A Electricity standard NML gas lubricated piston gauge calibration System (P04) NML direct resistance calibration system (E13)  Pa digital thermometer U = ℃ B NML resistance temperature detectors calibration system (T04) Temperature standard K SI unit length (m) Gauge Block Interferometer calibration system (D02) Frequency Stabilized Lasers calibration system (D16) Comparator calibration system (D01) Standard gauge block Stabilized laser Gauge block measurement result Gauge block measurement result Gauge block Temperature standard Pressure standard Temperature 、 pressure standard The triple point of water ： U = 0.21 mK Ga melting point ： U = 0.40 mK  The laboratories operating calibrations of relevant auxiliary parameters are all inner labs of NML and accredited by TAF.  Calibration intervals indicate on their calibration certificates issued by the laboratories. MeP Stabilized laser (Calibration certificate) 4. competence 6. calibration intervals

18 20 kHz Expanded uncertainty Document No. 20 nm to 33 nm 28 nm to 57 nm ICT: MSVP: ICT: MSVP: ICT: MSVP: SI unit length (m) Gauge Block Interferometer calibration system (D02) Frequency Stabilized Lasers calibration system (D16) Comparator calibration system (D01) Fequency stabilized laser, f  λ, wavelength ： nm Standard gauge block, L r 0.5 mm to 100 mm Gauge block measurement result Gauge block measurement result Measured difference, d 1 (  m ) Gauge block, L X 0.5 mm to 100 mm Deviation, d 2 (  m ) MeP Fequency Stabilized laser, f r, (Iodine stabilized He-Ne laser ) Note: 1.Instrument Calibration Technique, ICT: documented calibration procedure used in NML 2.Measurement System Validation Procedure, MSVP: calibration system evaluation report used in NML, within which the claimed uncertainty is recorded Metrological traceability of gauge block measurement - Complementary illustration in documentation  It shows complementary illustration including documented expanded uncertainties associated with documented ICT and MSVP in each traceability step at NML. 2. uncertainty of measurement 3. documentation

19 Discussion & Conclusion

20 Discussion & Conclusion Through the study activities for drawing metrological traceability diagrams combined with mathematical description, we will assure ourselves on knowledge transfer of gauge block and the other measurement systems with sufficient metrological know-how at NML. We will keep elaborating to further and deepen the concept of unbroken chain in metrological traceability to every measurement system of any kind quantities operating at NML. Since “reference to the SI units” is one of metrological traceability elements, derived quantity would be more complex than base quantity.

21 Thanks for your attention ~The End~